He also introduced the white dot inside each finger hole that later became a fixture of rotary phones. After the phone was redesigned at midcentury, with the letters and numbers moved outside the finger holes, users, to AT&T’s bewilderment, could no longer dial as quickly… With blank space at the center of the holes, Mr. Karlin found, callers no longer had a target at which to aim their fingers. The dot restored the speed.. (via df)